Method for producing alloy blanks

ABSTRACT

In order to provide a molten metal in a melting furnace with at least one alloy component or to increase the portion of the latter in the molten metal, a blank mixture has an alloy element containing the alloy component or being made of the latter, from water and a binding agent, and the blank mixture is processed into an alloy blank that can be placed in the melting furnace. At least as much water is added so that the blank mixture can be poured, and at least as much binding agent is added so that the alloy blank has a strength of at least 4/Nmm 2  after at the latest seven days setting time at 20° C., preferably at least 5 N/mm 2 . The blank mixture is poured into a casting mold and setting takes place without applying external pressing, with the alloy blank thus produced being removed from the mold.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY

This application is related to application number 10 2010 031 101.4-24, filed Jul. 8, 2010 in the Federal Republic of Germany, the disclosure of which is incorporated herein by reference and to which priority is claimed.

FIELD OF THE INVENTION

The invention relates to a method for producing alloy blanks in order to provide a molten metal in a melting furnace with at least one alloy component or to increase the portion of the latter in the molten metal, a blank mixture being produced using an alloy element containing the at least one alloy component or being made of the latter, from water and a binding agent, and the blank mixture being processed into an alloy blank that can be placed in the melting furnace. Furthermore, the invention relates to an alloy blank and to use of the latter.

BACKGROUND OF THE INVENTION

In the prior art it is known to specifically influence the composition of a molten metal in a melting furnace by adding alloy blanks which contain an alloy element in which one or more alloy components are present, either elementarily or in the form of a chemical compound. An example of this is the siliconising of iron melts in cupola furnaces with the aid of alloy blanks which, as an alloy element, contain a silicon carrier such as SiC or FeSi (see DE 1 583 262 B, DE 26 38 117 B, DE 196 02 486 C1, DE 199 17 008 A1). A further example is the addition of iron materials as an alloy element by means of alloy blanks containing the latter (see DE 44 16 699 A1, DE 297 03 389 U1, DE 1 143 837 B, DE 197 12 042 C1, WO 2005/118892 A1, DE 10 2005 062 036 A1) in iron melts, the addition taking place first and foremost for reasons relating to recycling. This can also be combined with the addition of silicon (see EP 1 624 079 A1). Such alloy blanks can also be used in vertical chamber reduction furnaces (see DD 139 601 C) or for coolant loading in steel converters (DE 25 01 636 A).

Moreover, it has been known for a long time to briquette certain materials, for example for forming clinkers in melting furnaces (see DE 43 08 294 A) and for disposal (see DE 42 07 265 A1).

The production of these blanks basically takes place in such a way that initially a blank mixture is formed which contains portions of alloy element, water, binding agent and an additive in the form of a support grain such as e.g. sand. This blank mixture is then compacted into the alloy blank, either in a stone compression mould or in a shaker (WO 2005/118892 A1). So that this is possible, the blank mixture must have a ductile or crumbly consistency. The water used here is measured such that it is just sufficient to bring about setting of the binding agent and to achieve the required consistency.

The compression of the blank mixture is a complex working process and requires the presence of a suitable press. With the aid of the press and the setting process the alloy blanks must become so solid that they can be placed as bulk material in a melting furnace and can pass through the melting furnace largely undamaged. The grain structure of the blank mixture is essential in order to achieve this solidity. Alloy elements in the form of dust, for example filter dusts or casting house dusts, cause difficulties here. Relatively coarse alloy elements, for example crushed scrap fragments, cuttings or the like are not ideal either. Difficulties with solidity also occur if a carbon carrier is processed as an alloy element.

SUMMARY OF THE INVENTION

Consequently, the object underlying the invention is to provide a method for producing alloy blanks which is inexpensive and with which alloy blanks can be produced using alloy elements with sufficient solidity, even in dust form or piece form.

This object is achieved according to the invention in that when producing the blank mixture at least as much water is added so that the blank mixture can be poured, and that at least as much binding agent is added so that the alloy blank produced from the blank mixture has a strength of at least 4 N/mm², preferably at least 5 N/mm², after at the latest seven days setting time at 20° C. and that the blank mixture is poured into a casting mould and setting takes place in the latter without applying any external pressing effect, and finally the alloy blank thus produced is removed from the mould. Consequently, the idea underlying the invention is not to compress the blank mixture, but to produce it by means of casting, a pourable blank mixture initially being produced, and the latter then being poured into a casting mould and being allowed to set, the aforementioned setting time starting when all of the blank mixture has been poured into the casting mould. It has been proved that with this method alloy elements both in dust form and in coarse pieces can be processed to form an alloy blank of sufficient solidity without this requiring the use of a press. The method can be implemented inexpensively and can be used for many purposes because it is suitable for alloy elements of a wide variety of types and many different grain sizes to the point of chunkiness.

Metals, even those of which the molten metal is substantially made, in particular iron, but also copper, zinc, chrome, manganese, nickel, molybdenum, titanium or vanadium, can be considered as an alloy element. The iron can also be in the form of iron alloys such as FeSi, FeMn, FeCr, FeNi, FeMo, FeTi or FeV. Metal oxides and ores, such as FeO, Fe₂O₃, MnO are also suitable. However, the alloying agent can also be a metallic silicon, for example in the form of SiC. Moreover, the method according to the invention is however also suitable for the processing of carbon carriers and/or uncombined carbon as an alloy element, for example graphite, coke breeze, petrol coke, pitch coke, compact dust etc. They can be used for the carburisation of the molten metal. Finally, the alloy element can also be a mixture of at least two of the aforementioned alloy components or alloy elements.

With the method according to the invention the lower limit for the added water is determined by the property of the pourability of the blank mixture. In general there is then sufficient water in order to guarantee setting of the blank, in particular—as known in the prior art—cement is used for this purpose. It is advantageous here for the purpose of preventing shrinkage holes in the alloy blank or insufficient filling of the casting mould, if as much water is added so that the blank mixture is self-running, in particular self-levelling in the casting mould. The latter is to be understood as the property whereby a level surface is established on the open side of the blank mixture poured into the casting mould, without any further measures, such as for example shaking or levelling off.

One should, however, note the fact that the solidity of the alloy blank with the same binding agent portion becomes less the higher the portion of water, i.e. it is a compromise between seeking good pourability of the blank mixture on the one hand and the ultimate solidity of the alloy blank on the other hand. For this it is helpful to add a fluxing agent, as is normally used when producing concrete, for example lignin sulfonate, melamine formaldehyde sulfonate, naphthalene formaldehyde sulfonate, polycarboxylates or hydroxycarboxylic acids and salts of the latter (see standard EN 934-2). The portion of the fluxing agent should come within the range of 0.01 to 0.5% by weight in relation to the weight of the blank mixture. By using the fluxing agent the water requirement for the purpose of producing the pourability is considerably reduced with the result that the alloy blank gains greater solidity or a smaller binding agent portion is required in order to achieve the minimum solidity according to the invention.

Good processability is produced when as much water and optionally fluxing agent is added to the blank mixture so that the blank mixture has a spread value (measured according to standard DIN EN 459-2, but without stroke thrusts) of at least 15 cm, preferably 19 cm, and advantageously no more than 21 cm. With values of 15 to 18 cm spread value shaking of the blank mixture in the casting mould is recommended for the purpose of preventing cavities between the casting mould and the blank mixture as well as shrinkage holes in the alloy blank. Advantageously the weight ratio of water to solid in the blank mixture should not exceed a value of 0.8.

The binding agents generally used for building materials, in particular hydraulic binding agents such as cement, can be considered as binding agents. Since the binding agent for the use of the alloy blank provided according to the invention constitutes a foreign material, the portion of the binding agent should not be very much higher than required in order to achieve the solidity provided according to the invention. It is therefore advantageous if the highest value cement possible is used because then the binding agent portion can be kept low. There is then a connection with the quantity of water added for the purpose of achieving pourability such that the quantity of binding agent must be higher the higher the water content. In order to achieve rapid setting one can also add to the cement a setting accelerator which accelerates the setting and hardening process. The addition of binding agent should not exceed 40% by weight in relation to the whole blank mixture, better it should however be no higher than 20% by weight, always with the proviso, however, that the aforementioned minimum solidity is achieved.

According to the invention provision is further made such that a support grain is added to the blank mixture. It should have a grain size of maximum 1.5 cm. Preferably sand should be used, and the support grain should advantageously be present with a weight portion of 5 to 40% in relation to the whole blank mixture.

Furthermore, the invention makes provision such that the blank mixture in the casting mould is shaken and/or the open surface of the latter is smoothed. Shaking is particularly recommended if the water content and optionally the fluxing agent content is so small the there is a risk of shrinkage holes forming or the casting mould not being completely filled.

So that insufficient setting or the formation of cracks does not occur in the region of the open surface of the blank mixture located in the casting mould the surface should preferably be sprayed with water immediately after the casting process. Alternatively or in combination with this, the surface can be provided with a covering impermeable to moisture or dispensing moisture.

The method according to the invention is suitable both for the use of an alloy element present in small piece form, preferably with an average extension of 0.5 to 5 cm, but also for an alloy element which is added in dust or powder form, in particular with a grain size of below 0.1 mm. Both forms of alloy element can be combined with one another here, preferably in a weight ratio of 20:80 to 80:20.

For the method according to the invention casting moulds can be used the internal volume of which corresponds to the predetermined shape of the alloy blank. Instead of this, however, a tub-shaped large mould can also be used, the interior of which is sub-divided into individual moulds, the large mould being filled with the blank mixture in a single casting process. Here the interior of the large mould can be sub-divided into the individual moulds by bars reaching up from its base. It is then possible to fill the individual moulds with the blank mixture so that the alloy blanks thus produced are separated from one another. Alternatively, the large mould can also however be filled to such a height that the open surface of the blank mixture lies above the bars, and so a one-piece structure in the form of a large blank similar to a (turned over) block of chocolate is produced. After removal from the mould this large blank is then broken in a breaker into individual pieces which form the alloy blanks. Breaking can also be implemented here by breaking the bars between the individual blanks so that the individual blanks thus formed form irregularly moulded blank pieces.

As well as the method according to the invention, the subject matter of the invention is also an alloy blank which can be obtained with the aid of the method described above, and to the use of this alloy blank by placing into a metal melting furnace when melting metal, preferably in a cupola furnace, converter, blast furnace or induction furnace.

Detailed Description of the Preferred Embodiment(s)

The following alloy blanks, for example, were produced by the method according to the invention.

EXAMPLE 1

SiC dust with a grain size <0.2 mm 35.97% ESiC80 with a grain size of 0.1-10.0 mm — Support grain with a grain size of 0.5-1.0 cm 21.58% Cement of the quality CEM I 52.5 N 14.39% (DIN EN 197-1) Fluxing agent on naphthalene base — Water 28.06% Spread value 16.4 cm Compressive strength after 7 days at 20° C.′  5.4 N/mm²

EXAMPLE 2

SiC dust with a grain size <0.2 mm 32.85% ESiC80 with a grain size of 0.1-10.0 mm 25.55% Support grain with a grain size of 0.5-1.0 cm — Cement of the quality CEM I 52.5 N 14.53% (DIN EN 197-1) Fluxing agent on naphthalene base  0.07% Water 27.01% Spread value 20.0 cm Compressive strength after 4 days at 20° C.′  5.0 N/mm² Compressive strength after 7 days at 20° C.′  6.4 N/mm²

EXAMPLE 3

SiC dust with a grain size <0.2 mm 32.61% ESiC80 with a grain size of 0.1-10.0 mm 25.36% Support grain with a grain size of 0.5-1.0 cm — Special binding agent 1 14.42% Fluxing agent on naphthalene base  0.07% Water 27.54% Spread value 20.3 cm Compressive strength after 2 days at 20° C.′  5.5 N/mm² Compressive strength after 7 days at 20° C.′  7.5 N/mm²

EXAMPLE 4

“ESiC80” is to be understood as a SiC raw material which contains 80% pure SiC, the remainder being non-reacted free C and SiO₂. The special agent 1 specified in Example 3 is the binding agent marketed by HeidelbergCement Baustoffe für Geotechnik GmbH & Co. KG under the name “CEM-ROCK 489”, whereas the special agent 2 specified in Example 4 is also marketed by Heidelberg Zement Baustoffe fur Geotechnik GmbH & Co. KG under the name “CEM-ROCK MFG”. 

1. A method for producing alloy blanks in order to provide a molten metal in a melting furnace with at least one alloy component or to increase the portion of the latter in the molten metal, a blank mixture being produced using the alloy element containing the at least one alloy component or being made of the latter, from water and a binding agent, and the blank mixture being processed into an alloy blank that can be placed in the melting furnace, characterised in that when producing the blank mixture at least as much water is added so that the blank mixture can be poured, and that at least as much binding agent is added so that the alloy blank produced from the blank mixture has a strength of at least 4 N/mm² after at the latest seven days setting time at 20° C., preferably at least 5 N/mm², and that the blank mixture is poured into a casting mould and setting takes place in the latter without applying any external pressing effect, and finally the alloy blank thus produced is removed from the mould.
 2. The method according to claim 1, characterised in that a metal, in particular iron, as well as iron alloy such as FeSi, FeMn, FeCr, FeNi, FeMo, FeTi, FeV, or copper, zinc, chrome, manganese, nickel, molybdenum, titanium, vanadiun, or as metal oxides and ores, such as FeO, Fe₂O₃, MnO, and/or a metallic silicon, especially in the form of SiC, and/or a carbon carrier and/or uncombined carbon, for example graphite, coke breeze, petrol coke, pitch coke, compact dust for the carburisation of the molten metal or a mixture of at least two of the aforementioned alloy components is used as at least one alloy element.
 3. The method according to claim 1, characterised in that as much water is added to the blank mixture so that the blank mixture is self-running, in particular self-levelling.
 4. The method according to claim 1, characterised in that a fluxing agent and/or an accelerator is added to the blank mixture.
 5. The method according to claim 1, characterised in that as much water and optionally fluxing agent is added to the blank mixture so that the latter has a spread value of at least 15 cm, preferably 19 cm and advantageously no more than 21 cm.
 6. The method according to claim 1, characterised in that the weight ratio of water to solid does not exceed a value of 0.8.
 7. The method according to claim 1, characterised in that the binding agent contains or is produced from a hydraulic binding agent, in particular cement.
 8. The method according to claim 1, characterised in that the addition of binding agent does not exceed 40% by weight, preferably 20% by weight in relation to the whole blank mixture.
 9. The method according to claim 1, characterised in that a support grain is added to the blank mixture, advantageously with a grain size of maximum 1.5 cm, the support grain preferably being sand, and in particular being present with a weight portion of 5 to 40% in relation to the whole blank mixture.
 10. The method according to claim 1, characterised in that the blank mixture is shaken in the casting mould and/or the open surface of the latter is smoothed.
 11. The method according to claim 1, characterised in that the surface of the blank mixture in the casting mould is preferably sprayed with water immediately after the casting process.
 12. The method according to claim 1, characterised in that the surface of the blank mixture in the casting mould, optionally after spraying with water, is provided with a covering impermeable to moisture or dispensing moisture.
 13. The method according to claims 1, characterised in that the alloy element for the production of the blank mixture is used in small piece form, preferably with an average extension of between 0.5 and 5 cm.
 14. The method according to claim 1, characterised in that the alloy element is added in dust or powder form, in particular with a grain size of less than 0.1 mm.
 15. The method according to claim 13, characterised in that the at least one alloy element is used both in small piece and in dust or powder form, and that the weight ratio of their portions is between 20:80 and 80:20.
 16. The method according to claim 1, characterised in that the blank mixture is poured into a large mould the interior of which is sub-divided into individual moulds which are filled with the blank mixture in one casting process.
 17. The method according to claim 1, characterised in that the blank mixture is poured into a large mould the interior of which is sub-divided into individual moulds which are filled with the blank mixture in one casting process and that the large mould is sub-divided into the individual moulds by bars reaching up, and the blank mixture is filled to a level higher than the bars, and that the large mould produced in this way is broken into individual chunky alloy blanks after hardening.
 18. An alloy blank with an alloy element, characterised in that it can be obtained by the method according to claim
 1. 19. The use of the alloy blank according to claim 18 by placing in a metal melting furnace when melting metal, preferably in a cupola furnace, converter, blast furnace or induction furnace. 